It sounds like she may be, you could see if her nipples are larger and pinker, that's a clear sign. She also might be very loving, and the increase in appetite and 'nesting' behaviour are all signs - but that would mean she was late into the pregnancy - so you should be able to see a swelling in her stomach.
Get the litter tray for sure, and maybe put it in the cupboard, or near, then see how she behaves. Could you ask your vet BTW?
